Spectratyping is a rapid method for measuring T cell responses on the basis of TCR receptor utilization. It consists of dividing the responding T cell on the basis of the V gene they express as well as the length of the antigen contact region referred to as the third complementarity determining region, CDR3. The technique consists of amplifying the cDNA corresponding to mRNA for one of the TCR chains and separating the amplification product on denaturing gels. Typically, a normal repertoire is represented by multiple bands corresponding to different CDR3 lengths, whose intensity follows a Poisson distribution. Upon stimulation with antigen, bands corresponding to TCR from cells that responded to the antigen show increased intensity. We expect that the core laboratory will perform over 1000 spectratypes/year in support of these three projects as well as in support of technical Aim 1 and perhaps some of the pilot projects. By centralizing these analyses we will allow the individual project leaders to focus on other aspects of the research they are pursuing. In addition the Core will guarantee reproducible data sets for all the research components of the Center.